1. Field of the Invention
The present invention relates to a discharge bulb to be used in a headlamp for a vehicle and a method of manufacturing the discharge bulb.
2.Description of the Related Art
Since a discharge bulb can carry out high luminance irradiation, it has recently been used in a headlamp for a vehicle very often.
As described in Japanese laid open publication Hei 11-176319, for example, there has been known a discharge bulb to be used in a headlamp for a vehicle which comprises an arc tube unit 102 including an arc tube 104 and a shroud tube 106 cylindrically surrounding the arc tube 104, and a plug member 108 for fixing and supporting a base end 102a of the arc tube unit 102 as shown in FIG. 6.
In such a discharge bulb, it is optically important that a discharge light emitting section 104a of the arc tube 104 is provided with a predetermined positional relationship with an optical datum plane Po of the plug member 108. For this reason, the arc tube unit 102 is fixed and supported on the plug member 108 in the following manner.
More specifically, a metal band 110 is fastened and fixed to the shroud tube 106 on the base end 102a of the arc tube unit 102, and furthermore, a slider fixture 112 is welded to the metal band 110. In such a state that the slider fixture 112 is set into a predetermined jig (not shown), the metal band 110 is caused to slide with respect to the slider fixture 122, thereby carrying out a necessary position adjustment. Thus, the welding is carried out in such a state that the discharge light emitting section 104a of the arc tube 104 and the optical reference plane Po of the plug member 108 have a predetermined positional relationship. Then, the slider fixture 112 is caused to abut on a metallic base plate 114 which is previously fixed to the plug member 108 and both of them are thus welded to each other. Consequently, the arc tube unit 102 is fixed and supported on the plug member 108.
In the conventional discharge bulb, however, there is a problem in that a structure for fixing and supporting the arc tube unit 102 on the plug member 108 is complicated, and furthermore, a manufacturing process is also complicated.
In addition, the metal band 110 is to be tightly fastened and fixed to the shroud tube 106 so as not to be loosened easily. Therefore, there is a problem in that the shroud tube 106 is often damaged, for example, broken by the fastening force.
The invention has been made in consideration of the circumstances and has an object to provide a discharge bulb capable of fixing and supporting an arc tube unit to a plug member with a simple structure in a simple process without damaging, for example, breaking a shroud tube, and a method of manufacturing the discharge bulb.
The invention achieves the object by such a structure that the arc tube unit is fixed and supported on the plug member through a predetermined glass tube.
More specifically, the invention provides a discharge bulb comprising an arc tube unit including an arc tube and a shroud tube cylindrically surrounding the arc tube, and a plug member for fixing and supporting a base end of the arc tube unit,
wherein a glass tube is fixed to the plug member, the base end of the arc tube unit is inserted in the glass tube and the shroud tube of the arc tube unit and the glass tube are bonded and fixed to each other.
Moreover, the invention provides a method of manufacturing a discharge bulb comprising an arc tube unit including an arc tube and a shroud tube cylindrically surrounding the arc tube, and a plug member for fixing and supporting a base end of the arc tube unit, comprising the steps of:
inserting the base end of the arc tube unit in a glass tube which is previously fixed to the plug member; and
bonding and fixing the shroud tube and the glass tube to each other in such a state that an amount of insertion of the arc tube unit is regulated in order to set a dimension between an optical reference plane of the plug member and a predetermined position of a discharge light emitting section of the arc tube to be a predetermined set dimension.
If the xe2x80x9cglass tubexe2x80x9d in which the base end of the arc tube unit can be inserted and which can be bonded and fixed to the shroud tube is used, a specific structure such as a length, a sectional shape or a material is not particularly restricted. Moreover, the method of fixing the xe2x80x9cglass tubexe2x80x9d to the plug member is not particularly restricted.
If the xe2x80x9cpredetermined position of the discharge light emitting sectionxe2x80x9d of the arc tube can be specified, a specific position thereof is not particularly restricted. For example, it is possible to employ a tip position of one of a pair of electrodes constituting the arc tube or a central position between a pair of electrodes.